O-GlcNAcylation Regulation of SNAP29-Dependent Autophagy Activation Dictates Chemoresistance in Gastric Cancer.

Chemoresistance remains a major obstacle in gastric cancer (GC) treatment, particularly to standard fluoropyrimidine and platinum regimens. O-GlcNAc transferase (OGT) and O-linked β-N-acetylglucosamine modification (O-GlcNAcylation) are frequently elevated in cancers, yet their specific role in GC chemotherapy remains poorly defined. Contrary to its typical oncogenic function, this study demonstrates that low OGT/O-GlcNAcylation is associated with resistance to 5-fluorouracil (5-FU) or oxaliplatin (OXA) in GC. Clinically, high OGT expression correlates with better prognosis in patients receiving fluoropyrimidine/platinum chemotherapy. Functionally, OGT knockdown or O-GlcNAcylation inhibition promotes chemoresistance both in vitro and in vivo. Mechanistically, OGT interacts with and O-GlcNAcylates synaptosomal-associated protein 29 (SNAP29) at Ser2, Ser61, Thr130, and Ser153. This modification inhibits STX17-SNAP29-VAMP8 complex assembly and autophagosome maturation. Molecular dynamics simulations suggest this involves disruption of inter-chain hydrogen bonds and increased flexibility at SNAP29 termini. Loss of SNAP29 O-GlcNAcylation relieves this suppression, enhances protective autophagy, and drives chemoresistance. Additionally, acute 5-FU or OXA treatment downregulates OGT and O-GlcNAcylation, potentially initiating a feedforward resistance loop. Importantly, elevating O-GlcNAcylation with Thiamet-G sensitizes GC tumors to chemotherapy in vivo. These findings reveal a context-dependent role for the OGT/SNAP29 axis in regulating chemoresistance via autophagy and nominate OGT as a promising therapeutic target in GC.